Index

SUBPT

Subtract checked pointer subtracts an optionally-shifted register value from a base address register value, and writes the result to the destination register. The optionally-shifted register value is treated as the offset.

If the operation would have generated a result where the most significant 8 bits of the result register differ from the most significant 8 bits of the base register, then the result is modified such that it is likely to be non-canonical when used as an address.

Integer
(FEAT_CPA)

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1 1 0 1 1 0 1 0 0 0 0 Rm 0 0 1 imm3 Rn Rd
op

SUBPT <Xd|SP>, <Xn|SP>, <Xm>{, LSL #<amount>}

if !IsFeatureImplemented(FEAT_CPA) then UNDEFINED;
integer d = UInt(Rd);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer shift = UInt(imm3);

Assembler Symbols

<Xd|SP>

Is the 64-bit name of the general-purpose destination register or stack pointer, encoded in the "Rd" field.
<Xn|SP>

Is the 64-bit name of the first general-purpose source register or stack pointer, encoded in the "Rn" field.
<Xm>

Is the 64-bit name of the second general-purpose source register, encoded in the "Rm" field.
<amount>

Is the left shift amount, in the range 0 to 7, defaulting to 0, encoded in the "imm3" field.

Operation

bits(64) result;
bits(64) base = if n == 31 then SP[] else X[n, 64];
bits(64) offset = LSL(X[m, 64], shift);

result = base - offset;
result = PointerAddCheck(result, base);

if d == 31 then
    SP[] = result;
else
    X[d, 64] = result;